Automatic transmissions may include a torque converter for coupling a transmission input shaft to a crankshaft of an engine. The torque converter includes an impeller fixed to the crankshaft, a turbine fixed to the input shaft, and a stator disposed between the impeller and the turbine. The torque converter may also include a bypass clutch that mechanically couples the transmission input shaft to the case of the torque converter, which is fixed to the crankshaft. The bypass clutch may include one or more clutch plates that rotate with the case and are interleaved with one or more disks that rotate with the input shaft. To engage the clutch, pressurized fluid forces a piston to compress the clutch plates.
The stator redirects fluid returning from the turbine so that the fluid is rotating in the same direction as the impeller. Some stators have variable-pitch blades that are controllable to alter the flow of fluid from the turbine to the impeller to tighten or loosen the torque converter.